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Hand Movements Give Your Poker Game Away

This is the lesson: What one thinks he is communicating hinges on a facial expression. Accordingly, a poker face is the expressionless gaze that gives nothing away. To win at poker, this idea counsels, one must master controlling an expressionless face.

In world poker tournaments the best players do their utmost to follow this adage. But a recent study published in Psychological Science by Michael Slepian and colleagues at Stanford University suggests that even those with the most stone–faced poker faces still give the game away. They do so not by their facial expressions, but with their hands.

Professor Slepian showed his students short video clips. Some depicted players from the table up; others just the face; yet others only the arms and hands. What he found was that students poorly judged a player’s hand when shown only the face. Statistically, the better a student judged the hand to be, the worse it actually was.

When a player’s whole posture was visible the misjudgment went away: Seeing everything about a player from the table up led to no correlation between a judgment of a hand and its actual value. When a student could see only arms and hands, however, Professor Slepian found a positive correlation of 0.07 between guesses and reality. This is extremely weak.

Even students who were poker novices could judge the quality of a professional player’s cards from the behavior of his hands. The question was, how? From previous studies Professor Slepian knew that anxiety tends to disrupt smooth body movements, and he suspected this might be the explanation. He showed a fresh set of volunteers the clips he had used in the previous experiment. Rather than asking to judge the quality of a player’s cards, however, he asked them to rate either the player’s confidence or how smoothly the player pushed his chips into the middle of the table.

He found that when students rated players as being confident or having hands that moved smoothly, the cards they held was likely to be good. A positive correlation of 0.15 held when students considered confidence, and 0.29 when they looked for smooth movement. They were more capable of determining hand quality from these variables than when asked to estimate it directly.

The moral is: don’t look your opponent squarely in the eye if you want to know how good his cards are. The secret of his hand lays in his hands.

Joe Navarro has done some work on this. It's an interesting topic. I haven't read his books on poker specifically, but his other work on body language makes it pretty clear that whole picture is far more important than just the face, much of which can be manipulated. Put on a hat and glasses, and get a botox injection, and your face isn't going to reveal much, but that nervous foot will still be jiggling away.

Right you are. The reason it is difficult not to broadcast what you are feeling is the same reason it is hard to maintain a poker face. But as the research you point out shows, BODY language in general often tips one's hand more than facial expression does.
Now the interesting question is, Why?

I'm going to guess two reasons: The first is that as social animals, we've been taught since childhood "put on a smile", be polite, pretend we like people we don't, appease stronger others, etc...which equates to being taught all our lives to lie with our faces. No one teaches us to lie with our shoulders, or our thumbs, etc. The face is where we are most conscious of our displays, and therefor most able to deceive with them.

The second is that we've had many thousands of years of evolution toward self preservation that will override our social conventions, so we can sometimes make our faces obey, but the rest of us is still responding to limbic arousal. No matter how confident you wish to appear in front of a group, they can still see your hands shaking and your feet pointed to the exits.